A judge in the Florida Keys has overturned the state's constitutional ban on same-sex marriage after a legal challenge by six gay couples said it effectively made them second-class citizens.

The judge ordered the clerk of courts office to begin issuing marriage licenses to gay couples.

The ruling was issued Thursday by Circuit Judge Luis M. Garcia and applies only to Monroe County, which covers the Keys. The lawsuit contended that the same-sex marriage ban approved by voters in 2008 violated the U.S. Constitution's guarantee of equal protection under the law.